1. What is meant by the half-life of a radioactive source?

2. Describe in detail a method of measuring the half-life of a radioactive element. Your description should include a labelled diagram of apparatus.

3. A decay curve of a radioactive element is shown below. Calculate the half-life of the radioactive element.

 

 

 

 

 

 

 

4. The activity of a source drops from 1000 kBq to 125 kBq in 9 days. What is the half-life of the source?

5. A source has an activity of 1800 kBq and a half-life of 2 days. What is its activity 10 days later?

6. A source has an activity of 800 kBq after being stored for 4 days. If the half-life is 1 day, what was its initial activity?

7. A radioactive isotope has an activity of 40 MBq and a half-life of 15 s. How long will it take for its activity to drop to 625 kBq?

8. A medical physicist carries out a shielding experiment to find out what kind of radiation is being emitted by unknown sources X and Y.
He sets up the following apparatus and records the results shown below.

(a) What kind of radiation is each source emitting? Explain your answer.
(b) What effect would sources X and Y have on photographic film?

The physicist thinks source X would be best to use as a radioactive tracer but has to ensure it has a suitably short half life.

(c) Why is source X better than source Y as a radioactive tracer?
(d) Why is it important to ensure the source has a short half life?

She carries out an experiment to determine the half life of source X and finds that the count rate falls from 3 200 Bq to 200 Bq in 3 hours.

(e) Calculate the half life of the source.
(f) What fraction of the sample would be left after 90 minutes?
(g) What would the activity of the source be after 90 minutes?